In a small saucepan over medium-low heat, melt truffle butter. Remove from heat, add the truffle oil and set aside.

Heat the duck fat and 1 popcorn kernel, over medium-high heat, in a large pot with a lid. As soon as the kernel pops, add the rest of the popcorn, cover the pot and shake over the heat—quickly moving the pot back and forth over the burner—until the popping stops.

Pour half of the popcorn into a large mixing bowl, removing any unpopped kernels. Drizzle half of the butter-oil mixture and sprinkle half of the cheese over the popcorn, tossing to evenly distribute. Repeat with the rest of popcorn. Season to taste with coarse salt and serve immediately.